The present invention relates to a high efficiency heated inclined separation pressure vessel used in the separation of oil emulsions.
Crude oil is product of an extractions process. Extensive geological and geophysical analysis identifies an oil bearing reservoir within the earth""s crust. Reservoir fluids are brought to surface and the components of the reservoir fluids are separated. Oil companies must produce a crude oil product that will be acceptable to the refineries. Most oil bearing reservoirs contain oil, gas, water, and solid particulate. Free water is easily removed from the reservoir effluent using a vessel commonly called a Free Water Knock Out (FWKO). Free gas is easily removed from the reservoir effluent using a vessel commonly called an Inlet Separator. However, some water, gas and solids remain bound up with the crude oil, known as emulsion. These emulsions are usually unacceptable to the refineries and therefore impurities in the oil must be removed. This final polishing process is achieved by various means; heated atmospheric tanks, heated pressure vessels known as emulsion treaters, hydrocyclones and centrifuges.
Once the free water and free gas is removed, the remaining emulsion is an oil continuous phase dispersed with water droplets, gas bubbles and solid particulate. Separation of water, gas and solids from the oil continuous phase is achieved utilizing the difference in densities of the individual components. The general relationship governing this process is expressed in Stoke""s Law.   V  =                              d          2                ⁡                  (                                    p              c                        -                          p              o                                )                            18        ⁢                  xe2x80x83                ⁢                  η          o                      ⁢    g  
Where: V=settling velocity
d=droplet/bubble/solid diameter of impurity
pc=density of impurity
po=density of oil continuous phase
xcex7=viscosity of oil continuous phase
g=gravitational acceleration
Obviously the factors that influence the separation are: water droplet diameter, solid particulate diameter, gas bubble diameter, density of water, density of solids, density of gas, density of oil, viscosity of oil, heat, settling distance, retention time and the force field the process is subjected to. Chemicals may also enhance the separation efficiency of an emulsion. Once the emulsion is contain within a closed conduit, the volumetric flow rate must remain within the laminar regime.
Heated atmospheric tanks are most commonly used for single well production for various reasons including; minimum capital expenditure and low flow rates. Refinery acceptable crude oil is easily achieved. Atmospheric tanks are limited by throughput (flow rate) and maximum process temperature.
Conventional heated treaters are most commonly used at central processing facilities for various reasons including; greater throughput and higher maximum processing temperatures. Conventional treaters usually fall into two broad categories; horizontal and vertical, each having its own advantages and disadvantages. The most significant disadvantage of conventional treaters is the method of heating. The heat source for conventional treaters has been the fire tube, consisting of a burner outside the vessel, pipe looped inside the vessel and a flue stack outside the vessel. The heat generated from combustion gases transfers to the emulsion by passing the combustion gas through the looped pipe inside the vessel. This heat transfer process is very inefficient due to combustion efficiency of the burner, loss of heat up the flue stack and gunge (consisting of coked hydrocarbon and solid particulate) that builds up on the outside of the fire tube (looped pipe) immediately after start up. A second disadvantage of the conventional treater is the channelling effect. It is well known that fluids will take the path of least resistance. The channel effect is well documented in various SPE papers. The third disadvantage of convention treaters is somewhat of a xe2x80x9ccatch 22xe2x80x9d. In the attempt to increase retention time and throughput industry has increased the diameter of the conventional horizontal treaters. Increasing the diameter increases the likelihood of channelling and increases the settling distance. One gains efficiency in retention but losses efficiency with channelling and distance travelled to clearly separate.
Canadian Patent 924256 describes an oblique elongate pressure vessel. The heat source is a fire tube runs coaxially the length of the entire vessel penetrating the pressure vessels upper and lower ends. Canadian Patent 911369 is similar to Canadian patent 924256, except that an electrostatic grid is used as the heat source. Canadian Patent 926342 describes a pressure vessel, generally horizontal, which has both a heat source and an electrostatic grid. U.S. Pat. No. 6,099,742 is similar to Canadian patent 924256, in that it also utilizes a fire tube. In U.S. Pat. No. 6,099,742 the burner is located at the upper end instead of the lower end of the pressure vessel and the flow paths are different. The U.S. Pat. No. 6,099,742 also adds a second vessel for the liberated solution gas. U.S. Pat. No. 5,837,152 (Canadian Patent Application 2202210) describes an oblique elongated pressure vessel.
What is required is a more efficient configuration of heated inclined separation pressure vessel.
According to the present invention there is provided a heated inclined separation pressure vessel which consists of an oblique elongate pressure vessel. The pressure vessel is closed at both ends with conventional pressure vessel heads, for receiving emulsion where the water, gas and solids are entrained within the continuous oil phase. The present invention incorporates a high efficiency heating transfer assembly, composed of a furnace and heat tubes, to decrease the viscosity of the continuous oil phase, providing a higher settling velocity. The heat tubes penetrate the lower pressure vessel head, run coaxially and concentrically through the vessel, terminated adjacent the upper end of the vessel. Heat transfer to the tubes, for evaporation of the heat tube fluid, is accomplished in the furnace adjacent to lower vessel end.
Although beneficial results may be obtained through use of the heated inclined separation pressure vessel, as described above, it is preferred that an elongated sleeve be positioned coaxially and concentrically through the vessel, enclosing the heat tube bundle. The lower end of the sleeve is open to vessel, while the upper end of the sleeve is closed with conventional pressure vessel heads. The sleeve has several advantages including; providing a chamber for efficient heat transfer from the heat tubes to the emulsion, decreasing the settling distance for impurities. The top half acts as a collector trough for the liberated gas, while guiding the gas to the gas separator. The bottom half acts as a collector trough for the liberated water and solid particulate, while guiding the impurities to the lower end of the vessel for removal.
Although beneficial results may be obtained through use of the heated inclined separation pressure vessel, as described above, it is preferred that a gas separator be located above the vessel adjacent the upper vessel end. The gas separator is defined as an elongated cylindrical pressure vessel, closed at both ends with conventional pressure vessel heads. Gas liberated from the sleeve chamber directed to the gas separator by the trough created by upper surface of the sleeve.
The present invention also includes various mechanical components which will hereinafter be further described including; roller assembly, pivot joint and removable support for timely cost effective maintenance overhauls.